1. Field of the Invention
The invention relates generally to venous grafts and in particular to a self adjusting equalizing graft.
2. Related Art
There are currently more than 400,000 patients in the United States with end-stage renal disease (ESRD) and many times more than that throughout the world. ESRD accounts for approximately 6.4% of the overall Medicare budget at over $23 billion dollars in the US in 2006. Patients with end stage renal disease have lost their normal kidney function and as a result require dialysis to substitute the function of the kidney cleansing the blood. There are two types of dialysis; hemodialysis and peritoneal dialysis. For purposes of this overview we will primarily be focused on hemodialysis and later discuss briefly the topic of peritoneal dialysis.
Hemodialysis requires that large volume blood access and exchange be consistently available to sustain the life of the patient. Typically, a dialysis patient will require 3-4 hours of dialysis three days a week. The challenge with providing hemodialysis is maintaining access to large volumes of blood when a body constantly fights attempts to keep access available by healing closed such access. Currently there are three ways to provide hemodialysis; dialysis catheters, arterial venous fistulas (AVF's) and arterial venous grafts (AVGs). Although used world wide, catheters are known not to be efficient for long term dialysis. Unfortunately, catheters have very short patency rates and high rates of infection. For these reasons dialysis guidelines strongly oppose catheter use, other than short term, until fistula or graft placement is available.
AVG's and AVF's are synthetic and natural conduits respectively that are surgically placed to provide long term dialysis access. Both provide large diameter targets that can be easily accessed with large needles for blood exchange. These conduits are commonly placed in the arm with the furthest point attached to the patent's artery and then are directly attached to the vein for blood flow return. The high arterial blood pressure and flow is shunted directly to the vein providing dilatation of the vein or graft and large volume blood flow. Although these methods provide excellent means of access both have limitations with regard to sustaining long term patency. The patency rates are much greater than that of a catheter however overall are relatively poor when considering the few years gained in a patent's life. It has been noted that there is only 50% shunt patency at one year and less than 25% at 2 years. Not only does this create a huge burden on the cost of healthcare but more importantly, once access is no longer available, a new access point must be created to sustain a patient's life.
A thorough description of the reason for dialysis fistula and graft failure is beyond the scope of this document. The fundamental problem is that the flow dynamics created by these artificial conduits are not normal to our bodies. The change is detected by the body and the normal physiologic defenses become involved and attempt to return the system to normal.
From the discussion that follows, it will become apparent that the present invention addresses the deficiencies associated with the prior art while providing numerous additional advantages and benefits not contemplated or possible with prior art constructions.